Portable circuit breaker tester for calibrating a circuit breaker over a wide range of current

ABSTRACT

A tester for circuit breakers in which the tapped primary of a power transformer is used in conjunction with the secondary of a voltage boosting transformer controlled by a variable transformer to generate current in the circuit interrupter to be tested. The range of current is continuously variable from zero to approximately 50,000 amperes. A device for measuring the duration of the current in the circuit interrupter is provided and a means for measuring quick surges of current which immediately trip a faulty or overloaded circuit interrupter is provided to determine duration of breaker engagement and maximum current flowing before interruption.

United States Patent Elder 1451 July 18, 1972 [54] PORTABLE CIRCUIT BREAKER 2,719,234 9/1955 Wright, Jr ..323/49 x TESTER FOR CALIBRATING A 1,967,849 7/1934 Wideroe (ER 11) 2,415,712 2/1947 St, Palley E 1 %%E,%% A E 2,830,255 4/1958 DBlaSiO.....

, 1,819,468 8/1931 Kroppehn 72 Inventor; Frederick A m Murrysvme, 3,179,875 4/1965 Keats ..323/43.5 R [73] Assignee: Westinghouse Electric Corporation, Pitt- P i E i r-A. D. Pellinen sburgh, Pa. Attorney-A. T. Stratton and C. L. McHale [22] Filed: April 7, 1970 ABSTRACT [21] A 26196 A tester for circuit breakers in which the tapped primary of a power transformer is used in conjunction with the secondary {52] US. Cl. ..'.323/45, 317/D1G. 5, 323/49, of a voltage ing r n rme ontr lled by a variable 324 23 transfonner to generate current in the circuit interrupter to be 51 Int. Cl. .0051 1/24 tested- The range of current is continuously variable from Zero 58 Field at Search ..323/6, 43.5 R, 44, 45, 48, to approximately 50,000 ampere-8 A device measufing the 323/49 duration of the current in the circuit interrupter is provided and a means for measuring quick surges of current which im- 56] Reerences Cited mediately trip a faulty or overloaded circuit interrupter is provided to determine duration of breaker engagement and max- UNITED STATES PATENTS imum current flowing before interruption. 687,147 11/1901 Fleming ..323/45 5 Claims, 8 Drawing figures United States Patent 1 78,372 Elder [451 July 18, 1972 I Ii IOB -J CIRCUIT BRE R UNDER TE D16 ITA VOLTNE OSC I L'LOGR APH PATENTEU JUL] 8 I972 SHEET 2 BF 6 l I l PATENTED JUL] 8 I972 SHEET [1F 6 208 TO 580V AC.

sum 5 OF 6 LEAKAGE LESS THAN 35 MICROHENRES IN PRIMARY (DHMS REMOVABLE Nh ALL RESISTORS 'NON-INDUCTIVE PATENTEU JULI 8 I872 FIG. 2D

PORTABLE CIRCUIT BREAKER TESTER FOR CALIBRATING A CIRCUIT BREAKER OVER A WIDE RANGE OF CURRENT BACKGROUND OF THE INVENTION This invention relates to circuit breaker testers and particularly to variable output circuit breaker testers used for determining the time-versus-current relationship of a circuit breaker under test. It has been the desire of those who build or use circuit interrupters or protectors to test them periodically. This is advisable because of the fact that components may age causing circuit breakers and interrupters to trip at undesired values of current. In addition, fire insurance underwriters require that circuit interrupters be tested relatively often. This leads to the result that confidence in the reliability of a circuit breaker is a function of how often it is tested. To this end among others, circuit breaker testing equipment of various types has been developed Circuit breaker testers are usually relatively large, mutlifunctional devices used either at the manufacturing plant or at the circuit breaker installation to simulate various circuit conditions which may occur in a circuit breaker and measure the results. On site testing requires disconnecting the circuit breaker from the protected circuit for at least a short period of time in order to connect the testing equipment to the breaker. On site testing is a practical way to test the equipment without resorting to a relatively long period of down time or lost service such as would be required if the equipment were transported back to the manufacturer for testing. Most types of circuit breaker testing equipment though multifunctional in nature have a common aspect, that of testing the current response of a circuit breaker with respect to time. Reference to the Pritchett US. Pat. No. 3,041,464 issued June 6, 1962 and the Craig U.S. Pat. No. 3,178,642 issued Apr. 13, 1965 shows that circuit breaker testing has developed to the point where the maximum power which a circuit breaker is capable of interrupting in actual service is not necessarily needed as input to the circuit breaker testing device. Rather, relatively low power is used to feed circuits which, in turn, generate the higher currents through the use of interposing transformers. Both of the named patents follow a similar pattern in that autotransformers or continuously variable transformers are connected to a relatively low power input source. The wiper or movable arm of the autotransformer is, in turn, connected to the primary of a transformer whose power rating is sufficient to induce relatively high currents into its secondary. The secondary is connected to the load or circuit breaker to be tested. It will be noted that an autotransformer is used as the means for varying the amount of current in the secondary of the main power transformer. lt is used rather than a potentiometer or variable resistance voltage divider because the resistance of the potentiometer would be reflected into the secondary of the power transformer and magnified by the inverse turns ratio to thereby prevent the flow of relatively high current in the secondary and also cause a phase shift between the secondary current and voltage. A variable transformer such as the type generally known under the trademark VARlAC" does not reflect high resistive impedance into the secondary of the power transformer and yet allows for voltage variation in the primary of the main transformer.

Known types of circuit breaker testers have problems which this invention is intended to overcome. The first important problem results from the fact that some means to vary current must be employed either in the primary or secondary circuits of the testing device. Usually an autotransformer in the primary circuit of the power transformer is used for this purpose. The standard wiring arrangements of the autotransformer is such that it is connected to a relatively lower power input source and the primary of the main transformer is supplied with power from the autotransformer movable contact. Therefore, the autotransformer must carry at least as much power as the main transformer. Although the primary of the main transformer is a relatively low current carrying winding compared with the current carrying capabilities of the circuit breaker to be tested, it must still be capable of handling power in the kilowatt range. This means that additional expense is required to provide an autotransformer capable of carrying the same or higher amount of power than that necessary for energizing the primary winding of the main transformer when the secondary circuit is carrying full load current. The second problem in known circuit breaker testers is less grave but nevertheless important. In order to determine the characteristic current-versus-time characteristic of a specific circuit interrupter, a measuring means must be incorporated into or associated with the testing means. Quite often a simple ammeter is used, but ammeters have inherent limitations of being capable of measuring currents only up to a certain value and through a small range without introducing a serious error into the readings. An alternative is to use a tapped multicontact switch in the secondary circuit of the main transformer. By doing this, special resistors can be placed into the ammeter circuit to compensate for higher values of current as the test is conducted over a wide range of current. It should be noted at this time that even though a low power testing device is commonly used, currents of up to 50,000 amperes may be required for such tests. The overall power rating of the tester is kept low by using low voltages when generating the high currents necessary. Nevertheless, the current required is sufficient to cause serious problems if appropriate measures are not taken to guarantee safe flow and accurate reading of this current. The use of a multi-tap switch introduces the problems of changing the impedance of the secondary circuit as the switch is changed from one tap position to another which causes an additional error in the measuring procedure which must either be compensated for or permitted to affect the test results. In addition, as the switch contacts become dirty and pitted, their resistive properties change so that as they age, the overall resistance of the circuit being tested changes even though the tap setting may be exactly the same. An alternative to this is to measure current by using the output terminals on the circuit breaker itself but this also has limitations in that one must then rely on the very device one is testing to provide the measurements being sought. A final problem arises in determining the amount of current that had flowed prior to a near instantaneous trip of the circuit breaker under test and at the same time determining for exactly how long the circuit breaker remained in a conducting condition. Many types of modern measuring equipment will not respond to a near instantaneous trip because of either electrical or mechanical momentum or inertia in the measuring circuit.

SUMMARY OF THE INVENTION In accordance with the invention, a means is provided whereby a circuit breaker or a similar device can be tested to determine its instantaneous tripping characteristic and its time-versus-current characteristic. A transfonner transfers power to its substantially low voltage, high current secondary. The secondary winding is in series circuit relationship with the circuit breaker to be tested. The principal embodiment of the invention allows for continuous variation of current from zero amperes to approximately 50 kiloamperes. This is accomplished in two ways. One, the primary of the main transformer is tapped in such a way that the number of windings and corresponding turns can be changed in discrete steps to induce corresponding discrete values of current into the secondary of the transformer. Two, continuous variation of current between each discrete step is accomplished by the use of a voltage boosting transformer which is connected in series with the tapped primary of the main transformer. One terminal of the primary of the boosting transformer is connected to one fixed terminal of the power supply and the other to the wiper of a variable autotransformer or Variac." The advantage of this arrangement is that the Variac" autotransformer need not carry the full amount of power required by the main transformer. The Variac autotransformer handles only that amount of power sufiicient to generate current equivalent to the difference between the largest discrete current steps. This means that a less costly Variac" autotransformer having a lower power rating can be used to accomplish the same purpose that was accomplished by the use of a Variac autotransformer capable of accommdating higher power in prior testers.

The problem of measuring the output current has been simplified by the use of a current sensing device such as a current transformer used with the secondary circuit of the main transformer. The current transformer is connected to a fixed load comprising a series of precision resistance combinations. The precision resistance combinations each has a tap such that a precision voltmeter can be connected by way of a switch across various combinations of resistance to account for or compensate for the changes in range of current being supplied by the secondary of the main transformer. This has the distinct advantage of keeping a constant load in the secondary of the main transformer over the entire range of current variation. It also eliminates unconnected ends on tapped switches of the type directly connected into the secondary circuit of the main transformer which could lead to electrical shock or burn of testing personnel. It also eliminates the problems of dirty or pitted switch contacts in a secondary circuit carrying high current. The fact that the load is constant and the current transformers inductance is constant, means that the phase shift introduced between the actual signal being measured by the voltmeter and the output reading can be calculated and reduced to a minimum to give a high degree of accuracy over the entire range of current in determining how much current is flowing in the secondary of the main transformer. The output of the current sensing device is not only connected to a voltmeter which is calibrated to read current but it is also connected to a timing circuit wherein a static device such as a silicon controlled rectifier (SCR) or thyristor is used to energize a relay coil which, in turn, starts and stops an accurate electrical timer. One important feature in this circuit is the fact that the power supplied to the circuit combination including the silicon controlled rectifier pulsates. This has the effect of turning the silicon controlled rectifier off" once per half cycle of power supply voltage. However, the signal being applied to the gate of the silicon controlled rectifier is received directly from the previously mentioned current sensing device. It is alternating voltage. lts frequency being the frequency of the current flowing in the secondary of the main transformer (usually 60 hertz). It has the property of turning the silicon controlled rectifier back on once every cycle. The relay coil of the timing circuit has a capacitor and a diode connected in parallel with it. They cause the coil to remain energized even though the silicon controlled rectifier is constantly changing states. The relay coil remains energized because the capacitor does not discharge as rapidly as the tum-on and tum-off" rate of the silicon controlled rectifier, even though it is this discharge which causes the timing circuit to work properly. When current has stopped in the secondary of the main transformer, the SCR turn-on" current will cease to be present at the gate of the SCR. Consequently, the capacitor, which has been charged by the previous half cycle of the pulsating input source, will completely discharge. As it discharges, the voltage across its terminals becomes smaller and finally reaches a point where it will no longer keep the coil of the timing relay energized. As this happens, the relay contacts will open, thus removing power from the electric timer.

A method is suggested in the preferred embodiment of the invention wherein a holding circuit is used to hold the highest voltage reading present at the. output terminals of the current sensing means. In addition, an oscillographic recorder is also connected to the output terminals of the current sensing means such that time can be recorded graphically. By the use of geometric scaling of the oscillographic record and a notation of the maximum voltage, important parameters in the near instantaneous interruption of a circuit breaker under severe overload conditions may be ascertained. Such parameters include the maximum current that has flowed, and the amount of time the circuit breaker under test was in a conducting state.

The purpose of the principal embodiment of the invention is to supply current, continuously variable over a wide range to a circuit breaker or interrupter to be tested without removing it a substantial distance from its normal working area. It is also a purpose to test a circuit breaker by the use of a novel current control device in the primary circuit of the main transformer. It is also a purpose of this invention to accurately measure the current induced into the secondary of the main transformer such that characteristic time-versus-current curves may be ascertained. The measuring device is of a type which affects the operation of the test circuit in only a minor way. Finally, a method is presented for determining the maximum current that flowed in a circuit breaker that was tripped almost instantaneously and the actual time before tripping.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention, reference may be had to the preferred embodiment exemplary of the invention shown in the accompanying drawings, in which:

FIG. 1 shows a simplified version of the circuit breaker tester;

FIG. 1a shows the main transformer in simplified form;

FIGS. 2A and 28 comprise a detailed schematic diagram of the invention; 1

FIGS. 2C and 2D show the same circuit shown in FIGS. 2A and 23 with some circuit parameters shown;

FIG. 3 shows a partial sectional somewhat diagrammatic view of a circuit breaker tester control panel; and

FIG. 4 shows the circuit breaker tester control panel.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings and FIG. 1 in particular, a i

simplified version of the preferred embodiment of the invention is a circuit breaker tester 7 shown between lines 8 on the left and 9 on the right. To the left of line 8 is a source of alternating current 10 which is adapted to supply the necessary power to the tester. Source 10 is connected to input circuit breaker 14 which controls the application of power to circuit breaker tester 7. Connected to the output terminals 15 and 16 of input circuit breaker 14 is an adjustable or variable autotransformer, Variac autotransformer or power dividing means 18. Autotransformer 18 comprises a set of terminals 20 and 22 which are connected respectively to output terminals 15 and 16 of input circuit breaker 14. The power dividing means or autotransformer 18 can be reversed where desired such that that terminal 20 is connected to terminal 16 and terminal 22 is connected to terminal 15. Autotransformer or variable mutual inductance device 18 has a movable contact point or wiper 24, capable of transversing or engaging any of the turns of winding 25 in autotransformer 18, which is con nected to output terminal 27.

Connected in circuit relationship with autotransformer 18 is a voltage boosting transformer 28. Boosting transformer 28 may also be used as a voltage bucking transformer if it is so desired. However, in the preferred embodiment of the invention, boosting transformer 28 is used only in a boosting mode. Boosting transformer 28 has a primary winding 30 with a plurality of turns 30W and a secondary winding 32 with a plurality of turns 32W. Secondary winding 32 has terminals 34 and 36 attached to the ends thereof and primary winding 30 has terminals 38 and 40 attached to the ends thereof. In the preferred embodiment of the invention, terminal 34 of the secondary winding 32 is connected to terminal 20 of autotransformer 18 and input circuit breaker output terminal 15. Terminal 38 of primary winding 30 is connected to terminal 27 or the wiper terminal of autotransformer l8. Terminal 40 of boosting transformer 28 is a common terminal and is connected concurrently to terminal 22 of autotransformer l8 and to the common terminal 16 of input circuit breaker 14.

Connected in circuit relationship with boosting transformer 28 is main transformer 42 which is the primary means for converting input power into high current, low voltage power suitable for testing a circuit breaker 64 or some similar circuit device. Main transformer 42 has a multitapped primary winding 43 with numerous turns or winding segments 43W. More specifically, primary 43W includes a winding portion 430 for coarse incremental adjustment of the output current and a winding portion 43f for fine incremental adjustment of the output current. Transformer 42 has an input terminal 44 which is connected to terminal 36 of the secondary winding 32 of boosting transformer 28. Attached to input terminal 44 is a wiper or movable contact 46. This wiper is capable of connection to any one of a plurality of tapped contacts such as 430a or 43cb. It is not limited to these specific contact points as there are many possible combinations of connections which can be used where desired. In the principal embodiment of the invention, the movable contact 46 generally is used to connect discrete sections of primary windings 43W to the output of transformer 28. Wound on the same magnetic core 48 as coarse winding 430 is fine winding 43]". At one end of coarse primary winding 43c is a terminal 47 to which is attached a movable contactor or wiper 52 similar to wiper or contactor 46 described previously. Wiper 52 can be moved from one group of discrete windings to another, as an example to points 43fa and 43/11, thus connecting or disconnecting groups or clusters of coils to terminal 47 and consequently increasing or decreasing the size or effective member of turns of primary winding 43 in a discrete fashion. Main transformer 42 has a secondary winding 54 wound on the same magnetic core 48 as primary winding 43. Main or power transformer 42 has output terminals 56 and 58 attached to secondary winding 54. Terminal 56 is connected to a first circuit breaker tester output terminal 59 whereas terminal 58 is connected to a second output terminal 61 through line or conductor segment 62 which is monitored or surrounded by current transformer 63 which is disposed in inductive relation with the line 62. The circuit breaker to be tested 64 is also connected to output terminals 59 and 61.

Current transformer 63 is connected at its output to current conversion and control means 65 at its input terminals 66 and 67, respectively. Current conversion and control means 65 has a set of output terminals 68 and 69 which are capable of being connected to voltmeter 72, digital voltmeter 74 and oscillograph 76 simultaneously or separately, as may be required. In addition, current conversion and control means 65 is connected by a data or electrical transmission link 80, preferably being an electrical conductor or a group of electrical conductors, to a timing circuit 90. Timing circuit 90 receives operating power through transformer 96T which has a primary winding 92 and secondary winding 94 disposed on the same magnetic core 96. Secondary winding 94 is connected to rectifier unit 97 which in turn supplies pulsating power to timing circuit 90. Primary winding 92 may be connected to the input circuit breaker 14 at terminals 15 and 16 respectively to utilize a single source of power for the tester 7.

Referring now to FIG. 1a, a simplified version 42' of transformer 42 is shown. It will be noted that the numbers used to identify parts or components of transformer 42' are identical to those used in describing transformer 42 except for the addition of a prime.

Transformer 42 has a primary winding 43 with a first input terminal 44', a magnetic core 48', and a second input terminal 49. Also wound on core 48' is secondary winding 54. Secondary winding 54 has output terminals 56 and 58'. Assuming that a suitable source 10 is connected to primary winding 43' at terminals 44 and 49', a voltage V1 is developed across these terminals when a current 11 flows in the winding 43'. Also assuming a suitable load 64' is connected to output terminals 56' and 58 of secondary winding 54, a voltage V2 is developed across these terminals and current 12 flows through load 64. Transformer 42' having primary turns N 1 and secondary turns N2 produces circuit operating characteristics as V2 K "12 In addition, the classical transformer equation applies:

Therefore,

V2 Vl N2/Nl (3 But N2 is fixed in this invention and therefore is a constant in equation (3). Therefore,

V2 K V1/N1 Now combining equations (4) and l it is seen:

K"I2 K'Vl/Nl rearranging the equation or more specifically I2=KV1/N1,whereK=K'/K" (7) Therefore, it can be seen that the current flowing in secondary 54 is inversely proportional to the number of turns N1 in primary 43 and directly proportional to the voltage V] impressed on primary 43.

Referring again to FIG. 1, considering the operation of the circuit interrupter testing means 7, power supply means 10 provides pulsating power, such as 60 hertz alternating power or voltage which is controllable by input circuit breaker 14. Depending upon the operating conditions of the primary of the main transformer 42, the boosting transformer 28 and, the power dividing means or autotransformer 18, a current 12 is induced into the secondary winding 54 of the main transformer 42. If contactors 46 and 52 of main transformer 42 are aligned such that all of the turns of the primary windings 43c and 43f are in series with terminal 36 of the secondary of boosting transformer 28 and boosting transformer 28 is producing substantially no voltage across its secondary winding 32 because its primary winding 30 is being supplied virtually no power because of the operating position of wiper or movable contact 24 on autotransformer or power divider means 18, then minimum current 12 will flow in secondary 54 of main transformer 42. If variable tap connector or contactor 46 is changed to another position, 430a as an example, less turns are in series with terminal 36. As a result, current I2 increases according to equation (7). In turn, according to equa tion (7), if wiper or movable contactor 52 is changed from the position shown in FIG. 1 to position 43fa, as an example, then even less turns are present in primary 43 of transformer 42 thus increasing current 12 even more. Regardless of the settings of variable contactors 46 or 52, the voltage between terminals 44 and 49 of transformer 42 equal the sum or total of voltage present between terminals 15 and 16 of circuit breaker 14 and the voltage between terminals 34 and 36 of boost transformer 28. Since this voltage can be varied continuously because of the action of wiper or variable contact 24, current I2 can be made correspondingly larger. This corresponds to increasing V1 in FIG. la and equation 7). Therefore, the combination of transformer 42, autotransformer 18 and boosting transformer 28 can be varied in such a manner that all values of current between zero and some maximum limit are obtainable. In the present embodiment of the inven tion, the design of transformer 42 is such that when used as described, a maximum current of 50,000 amperes or thereabouts can be obtained in the secondary winding 54 of transformer 42 and can be applied to circuit breaker 64 for testing purposes.

Current conversion and control means 65 is so designed that current 12 as sensed by current transformer or loop 63 is converted to a voltage which is displayed as amperes on a voltmeter 72, a digital voltmeter 74 or an oscillograph 76. In addition, a voltage signal is supplied through line or conductor 80 to timing circuit 90 which is designed to measure accurately the length of time that current 12 flows in the secondary 54.

Referring now to FIG. 2, a detailed embodiment 107 of the invention is shown. A source of alternating current power 110 is connected to a circuit breaker 114 having output terminals 115 and 116. Connected to terminals 115 and 116 are terminals 120 and 122, respectively, of autotransformer section 118. Transformer section 118 is comprised of two autotransformers 125T and 1253 serially connected at junction point 125C which acts as an output current vernier. Each of the autotransformers 125T and 1248 has a wiper or movable contactor 124T and 1258, respectively, joined by a linking means 124L to form a ganged moving set of contactors controlled by 'a dial 124D. The movement is such that when wiper 124T 1 moves toward terminal 120, wiper 124 moves toward terminal [122. This constitutes a differential output autotransformer section 118 rather than one which is necessarily grounded or made common to a common chassis connection. Wipers 124T and 124B are further connected to junction points 138A and 1408 respectively such that primary windings 130T and 1308 of voltage boosting transformer 128 may be connected either in series or parallel depending upon the current-voltage relationship desired at circuit breaker 164 which is to be tested. Winding 130T is connected at opposite ends to junction points 138A and 140A, and winding 130B is connected at opposite ends to junction points 138B and 140B. In the deenergized state of control relay 203K, contacts 203KA and 203KC are closed, while contact 203KB is opened. The result of this is to connect point 138A to point 1388 and point 140A to point 1408. This places primary windings 130T and 1308 of boosting transformer 128 in parallel circuit relationship with respect to the previously mentioned wipers or movable contacts 124T and 124B respectively, on the autotransformer 118. The secondary windings 132T and 132B of boosting transformer 128 are connected serially through relay contact 204KA of control relay 204K to circuit breaker 114 at terminal or junction 115 and also to the primary windings 143 of main transformer 142 at terminal point 136A. The secondary 132 also has a contact or terminal 136B the use of which will be described later. With respect to the part of the secondary 132 of transformer 128 connected to circuit breaker terminal 115, relay contact 204KA is closed or opened for the purpose of energizing or deenergizing, respectively, the circuit containing the secondary windings 132T and 1328 depending on the type of circuit arrangement relationship desired. Under most circumstances, control relays 204K and 205K are energized and control relay 207K is deenergized. This causes normally open relay contacts 204KA and 205KA to be closed and normally open relay contacts 207KA and 207KB to be open. In this circuit alignment, power supplied by source 110 passes through closed circuit breaker 114 at terminal 115, closed relay contact 204KA, secondary windings 132T and 1323 of transformer 128, the primary windings 143 of transformer 142, the closed relay contact 2051(A and back to circuit breaker 114 at terminal 116 and to the source 110.

Main transformer 142 comprises three sets of primary windings 143 designated coarse" as indicfid by 143C, iii? (right) as indicated by 143FR and fine" (left) as indicated by 143FL. All three windings are capable of various connections and are wound on the same magnetic core 148 with the secondary winding 154. The windings 143C, 143FL and 143FR are tapped such that groups of discrete primary coils or turns exist. Various taps are indicated in FIG. 2, as for example 143A, 1438, 143D, 143E and 143F, etc. Mounted in proximity with each of the sets of discrete tapped primary coils or windings is an associated bus bar. Specifically, bus bar 146 is located in proximity with coarse adjustment coils or windings 143C, bus bar 152L is located in proximity with fine adjustment coils or windings 143FL and bus bar 152R is located in structural proximity with fine adjustment coils or windings 143FR.

Referring to FIG. 3, connections between discrete groups of windings may be made by inserting at least one movable electrically conducting means 300, such as a copper slug, into a guide or hole 302 in insulated member 304 such that contact is made between tapped connector 143K and the associated bus bar 152L, as a specific example. One end 300T of slug or conductor 300 is insulated by insulating handle 306 for operator safety.

Referring again to FIG. 2, it is usually desirable to start any test on circuit breaker 164 at a low value of current 12. Therefore the maximum number of turns is required in the primary of transformer 142 as can beseen by reference to equation (7). Placing a plug or copper conductor 300 into tap 143E and onto bus bar 152R partially accomplishes this. However, it is also necessary to place a similar plug or slug 300 onto tap 143A and onto bus bar 146. This connects all available primary windings or turns in series circuit relationship with boosting transformer 128 and input circuit breaker 114. The placement of plug 300 into guide 302 associated with tap 143A also has a secondary purpose. Plug 300 engages and actuates switch or relay 20083 to the closed position whereby the relay coils 204K and 205K are deenergized and the relay coil 207K is energized. The effect of deenergizing coils 204K and 205K is to open contacts 204KA and 205KA, respectively. The effect of energizing the coil of relay 207K is to close associated contacts 207KA and 207KB. The end result of inserting plug 300 as described is to remove the secondary windings 132T and 132B of boosting transformer 128 from the previously mentioned series circuit between points or terminals and 144. Concurrently, the return path from the primary 143 of main transformer 142 between junction point 280 and circuit breaker terminal 116 is interrupted by the opening of contact 205KA. New circuit paths are established. The closing of con tact 207KA provides an alternate return path from junction point 280 to autotransformer 118 rather than to circuit breaker 114. This return path connects junction point 280 with the movable contactor or wiper 124B. Similarly, junction point 136B which is electrically connected to junctions 136A and 144 is connected through closed contact 207KA, and junction point 138A to movable contactor or wiper 124T.

In summary, the effect of placing a plug 300 in guide 302 such that terminal 143A on the coarse set of windings 143C is made to come into contact with bus bar 146 is to remove the entire set of primary windings 143 of transformer 142 from the terminals 115 and 116 of circuit breaker 114 and place it across the two ganged variable contacts or wipers 124T and 1243 of autotransformer 118, at the same time remove the secondary windings 132T and 132B of transformer 128 from the previously mentioned series circuit. As a result, autotransformer 118 carries the entire amount of power supplied to transformer 142 and the continuous control is gained by the sweep of movable contacts 124T and 1243 across the windings T and 1253 respectively of autotransformer 1 18. This particular circuit arrangement of circuit breaker tester 107 is only employed when the lowest possible values of current 12' are desired to flow in circuit breaker 164. If a greater amount of current is sought to flow through circuit breaker 164, less primary turns 143 are used in transformer 142. This requires moving the metallic slug 300 from coarse tap 143A to some other coarse tap, such as 1436. This removes all windings between junction point 282 and tap 143A from the primary 143 of transformer 142. The slug 300 again makes contact with bus bar 146, but microswitch 20083 which had been previously depressed or closed by placing the partially insulated slug 300 into the guide 302 associated with tap 143A is reopened. When this occurs, the normal circuit arrangement previously described for the primary 143 of transformer 142, the primary 132 of boosting transformer 128 and autotransformer 118 is reestablished. This is brought about by the reenergization of relay coils 204K and 205K and deenergization of relay coil 207K. In this situation, the circuit is completed through the main transformer 142 from point 144 through the fine control windings 143FL on the left to junction 282 to tapped connector 143G. At that point, bus bar 146 completes the circuit to the fine control windings 143FR on the right, through the entire set of fine control windings 143FR to point 143E which as previously mentioned has a partially insulated copper conductor or slug 300 to complete the circuit between junction 143E and bus bar 152R, whereafter the circuit path is completed through bus bar 152R to point 280 and from point 280 through contact 205KA and finally to the return terminal 116 of circuit breaker 114. Regardless of the position of the movable slug 300 between tap contacts 143A and 1438, the previously mentioned circuit arrangement will prevail.

It is expected that normally the current l2 supplied to circuit breaker 164 will be increased in discrete steps by moving the partially insulated copper slug 300 along bus bar 146 from contact 143A through 143G to 1438 and all the intermediate steps in between as shown in FIG. 2. At each step, an additional increase of current I2 in the secondary winding 154 of transformer 142 can be provided by variation of autotransformer 118 such that contactors or wipers 124T and 124B are moved in a manner as to provide increasing voltage across the normally shunt connected primary windings 130T and 130B of boosting transformer 128 so as to induce an ever increasing but continuously controllable voltage into the secondary windings 1328 and 132T of transformer 128. When the partially insulating metallic pin 300 is placed into hole or guide 302 associated with contact 1433, such that contact 1438 is electrically connected to bus bar 146 another variation from the normal circuit arrangement in transformer 143 results. The action of inserting pin 300 into proximity with contact 1438 and bus bar 146 produces two results. First, as can be seen by examination of FIG. 2, all coarse adjustment windings 143C are removed from the primary of transformer 142. Secondly, switch 20084 is engaged and actuated or caused to close. The closing of contact 20084 causes energization of relay coil 206K. This, in turn, causes normally open contact 206KA to close which joins bus bars 152L and 152R in parallel circuit relationship at junction 280. Junction point 144 is now connected directly to windings 143FL and through slug 300, tap 1433 and bus bar 146 to transformer winding 143FR. It will be remembered that windings 143FL and 143FR may be connected to bus bars 152L and 152R at points 143K and 143E respectively. Consequently, as more and more current is required in the secondary 154 of transformer 142, the two pegs or partially insulated conductors 300 may be moved in a direction from 143K and 143E, respectively, toward contacts 1431-1 and 143.], respectively, passing through points 143D and 1431*, respectively, along the way. Referring to FIG. 4, it is anticipated that these pegs or slugs 300A and 300B should be moved row by row simultaneously, but the invention is not necessarily limited to this method of connection. One terminal or slug may be moved at a difierent rate and to a different position than another peg if necessary. Referring again to FIG. 2, when the pegs have been moved to taps 143D and 143F, all terminals and the associated windings between taps 143D and 143K with respect to bus bar 1S2L and 143F and 143E with respect to bus bar 152R have been eliminated. This results in a smaller number of turns in the primary 143 of transformer 142. As mentioned previously, the voltage boosting of transformer 128 is still available in this particular circuit arrangement as nothing has changed in that particular part of the circuit. Finally, the two pegs or conductors 300A and 3008 can be moved to make contact between points or tapped connectors 1431-1 and bus bar 152L; and between tap or contacts 143] and bus bar 152R respectively. In this situation, every winding section in the primary 143 of transformer 142 has been removed with the exception of two, namely those two connected in parallel between points 143111 and 1431 and point 144. This represents the least number of turns which may be included in the primary of transformer 142 and corresponds to near maximum current 12' in the secondary 154 of transformer 142. The greatest current in secondary 154 occurs when the movable contacts or wipers 124T and 1248 of autotransformer 118 are moved to provide full voltage from autotransformer 118 at windings 125T and 1258 across primary windings T and 1308 of boosting transformer 128 thus inducing maximum voltage into the secondary windings 132T and 132B of boosting transformer 128. Under these circumstances, it has been found that currents in the range of 50,000 amperes can be provided in the secondary winding 154 of transformer 142 depending upon the characteristics of circuit breaker 164. It should be kept in mind that when using the coarse adjustment winding 143C as described previously, finer control can be achieved by using the movable metallic plug 300 associated with bus bar 152R and fine adjustment winding 143FR to add and remove various fine control turns from the primary winding 143 of transformer 142. in conjunction, the boosting transformer 128 can be used to given continuous variations over a relatively small current range.

Circuit interrupter testing means 107 has its own voltage supply and regulating means which derive power from the output of circuit breaker 114 at terminals 116 and 115. Voltage selector means 216 is connected by conductors to the terminals 115 and 116. This voltage selector means has the capability of supplying output power through a transformer 1961 to a pair of secondary circuits which include a secondary winding 191T which feeds a rectifier network 197 and a secondary winding 191B which feeds alternating power to various devices requiring a source of alternating current to operate. The voltage selector means 216 is provided to give circuit breaker tester 107 a capability of using different sources of power or voltage 110. Typically, power source 110 may be a 208, 240, 440 or 550 volts alternating current source. The voltage selector means 216 comprises a multitapped primary transformer 196T which is adapted to be connected to any of the above-named voltages but which is not limited to those mentioned and to supply power to the previously named secondary windings 191T and 1918. Full wave bridge rectifier 197 connected across the secondary winding 191T of transformer 196T is filtered by a capacitor 198 which has the special property of filtering the resulting direct output current in such a way as to preserve some of the pulsations that are naturally present at the output of a full wave rectifier, and yet to supply current of sufficient nominal magnitude to maintain the energization of the various circuit components including the relay coils previously mentioned. The reasons for the undulating output of bridge 197 will be explained hereinafter. Typically, secondary winding 191T of transformer 196T may be a 28 volt winding but is not limited exclusively to that particular value. Consequently, the output of the bridge rectifier network 197 is a nominal 28 volts peak and is used to energize all devices in the circuit breaker tester 107 which require a nominal 28 volt direct current. Secondary winding 1918 of transformer 196T is a 1 10 volt AC winding which is used to energize all devices and means in circuit breaker tester 107 which requires alternating energization at 1 10 volts. Connected in series circuit relationship with secondary winding 191T and rectifier circuit 197 is a normally open contact 201KB. Contact 201KB is actuated by the energization of coil 201K, through the closing of push-button switch 211. Push-button switch 211 is connected in parallel with a set of terminals such that a remote switch 211A may be used. Push-button switch 211 is also connected in parallel with contact 201KA such that when coil 201K has been energized due to the closing of switch 211, the contact 201KA acts as a holding circuit to maintain the energization of coil 201K regardless of the subsequent position of push-button starting switch 211. This is the means whereby the circuit breaker tester 107 is turned on or oft as power to the rectifier circuit 197 is controlled by the engagement or disengagement of contact 201KB. If contact 201KB is disengaged or open because pushbutton switch 211 has not been actuated to energize coil 201K, the elements which require a 28 volt supply will be without a source of electrical energy. Consequently, relay contacts 204KA and 205KA will be open thus preventing any transfer of power from terminals 115 and 116 of input circuit breaker 114 to the primary 143 of transformer 142 and, in turn, to the secondary 154 which is the main power circuit for test circuit breaker 164. Engagement of switch 211 and consequent energization of coil 201K supplies power to bridge rectifier network 197. This may be indicated by a flashing illuminated light 278 connected to output terminals 197N and 197? of bridge rectifier network 197. The illumination of this bulb indicates that circuit breaker tester 107 has been energized and power is being supplied to the secondary 154 of transformer 142. Until an initial engagement of starting pushbutton switch 211 and subsequent energization of relay coil 201K takes place, power is available at the output terminals 116 and 115 of input circuit breaker 114 but is not available at other various critical network components of the tester 107, such as boosting transformer 128 and main transformer 142. The presence of power at terminals 115 and 116 may be indicated by an indication on meter 222 and illumination of indicating light 270 shown connected across secondary winding 191B.

Usually, the primary windings 130T and 130B of boost transformer 128 are connected in parallel or shunt circuit relationship but are capable of being connected in series circuit relationship depending upon the operating positions of contacts 203KA, 203KC, 203KB of control relay 203K. The primary windings 130T and 130B of voltage boosting transformer 128 are electrically insulated to withstand voltages up to 800 volts or slightly larger. However, for input voltages in the 550 volt range or above, it is advisable to rearrange the connection of the two transformer primary windings 130T and 130B from a parallel circuit relationship with respect to the wipers or movable contacts 124T and 124B of autotransformer 118 to a series relationship with respect to each other and to the above wipers because of the inherent saturation characteristics of the magnetic core 130K. Consequently, only one half of the wiper voltage or potential will be applied across each of the windings. To accomplish this a voltage sensing relay 203K is made part of voltage selector means 216. When the voltage selector means 216 is in the 550 volt position, the coil of relay 203K will be energized thus changing the relative positions of the normally closed contacts 203KA and 203KC to the open positions and the normally open contact 203KB to the closed position. This changes the connections of the primary windings 130T and 1303 of boosting'transformer 128 from parallel circuit relationship to series circuit relationship. The voltage induced into the secondary coils 132T and 1328 of boosting transformer 128 doubles.

it is particularly desirable to protect the primary and secondary windings of transformer 142 against short circuits between said windings. In the event that such a short circuit should occur, it is detected and all power can be removed from transformer 142 to protect it, the related circuitry, and circuit breaker 164 under test. The means for indicating this is shown in FIG. 2. A lamp 220 glows or is illuminated should a short circuit develop between any of the primary coils or windings 143 and the secondary coil or winding 154. This is accomplished because an electrical conducting path exists between ground or common point 143C and ground or common point 2206. The path continues through transformer core 148 and the intrinsic capacitance 278 between the primary winding 143 and core 148. The path is further continued through secondary winding 154, resistor 218 which is connected at junction 156 to secondary winding 154, lamp 220, and the previously mentioned common or ground point 220G. Should a short circuit develop between primary and secondary windings 143 and 154, of transformer 142, the above described path would be a complete electrical circuit and the lamp or light 220 would illuminate due to the energization provided by the short circuit current.

Secondary winding 154 comprises a plurality of secondary winding turns 154W and is connected to the circuit breaker 164 under test at terminals 159 and 161. A manipulation of various current controlling devices in the primary circuit of transformer 142 provides a continuously controllably current variable from zero to approximately 50,000 amperes in the secondary winding 154 as previously described. This current is given the designation 12. In a circuit segment between terminals 161 and junction point 158 of the secondary circuit lies a conductor segment 162 around which is placed or disposed a current transformer winding 163. This current transformer or current sensing means 163 is connected at terminals 166 and 167 to a current conversion and control circuit 165, Conversion circuit 165 has four resistive components connected in series circuit relationship between terminals 166 and 167 of the previously mentioned current transformer 163. These are the resistive networks 224, which may be comprised of parallel resistive elements forming a single series resistance; and a special shorting link 224L, the use of which will be described later, resistive element 226, which is typically comprised of precision resistors connected in series circuit relationship, resistive element 228 and resistive element 230. Each of these resistive elements or means is separably connected to a tapped output terminal 224T, 226T, 228T, and 230T and connected to a multicontact switch 234 with contacts 232 to which each tap or tapped terminal is connected. Switch 234 is adaptable to selectively engage any of the four tap connections one at a time. Switch 234 forms part of an output network with output terminals 281 and 281A. It will be noted that the resistive components 224, 226, 228 and 230 are always present as a load for current transformer or loop 163 and regardless of the position of the tapping wiper or contactor 234W of switch 234 the inherent low resistance of the series network containing the named resistive elements carries most of the current flowing through current transformer or sensor 163. A relatively large amount of current is diverted from flowing into wiper 234W of switch 234 because of the inherent high input impedance of the measuring devices which may be connected to output terminals 281 and 281A, or the open circuit between terminals 281 and 282 should no measuring devices be connected. Consequently, the current flowing through the above resistive elements produces a voltage across each resistive element; it is combinations of this voltage which are placed across terminals 281 and 281A by switch 234. Ideally, resistive elements 224, 226, 228 and 230 are precision resistors of low error thus guaranteeing an accurate measurement of current by measuring voltage at the terminals 281 and 281A and calibrating the measuring devices to read current.

One of the measuring means connected to output terminals 281 and 281A is a timing circuit indicated at 190. Timing circuit or means is energized by the 28 volt full wave bridge rectifier network 197 which has the special quality of purposely having a rather poor filter. When power is supplied to the circuit breaker to be tested in the manner previously described, alternating current 12 flows in secondary 154, is sensed by the electromagnetically linked current transformer 163 and is converted to an alternating voltage signal by a current-to-voltage conversion means 165 such that a voltage is present between terminals 281 and 281A. This alternating voltage is supplied to the input terminals 283 and 284 of the timing circuit 190. Timing circuit 190 is comprised of a gated electronic valve such as a thyristor or a silicon controlled rectifier (SCR) or similar static gated device 241 with cathode 240, gate 242 and anode 244. Connected between terminals 283 and gate 242 is a variable resistor 236 to control the gate current and consequently control the turn-on characteristic of the silicon controlled rectifier 241. Connected to the anode 244 of silicon controlled rectifier 241 is a combination of elements connected in parallel circuit relationship comprising a relay coil or means 250 with intrinsic resistance 252, a diode 260 with cathode 264 and anode 262, and a holding capacitor 254. The other end of this parallel combination is connected to terminal 286. The output terminals 197N and 197? of the power supply 197 are connected to timing circuit 190 at points or terminals 284 and 286 respectively.

In the operation of the timing circuit 190, the alternating or undulating voltage supplied to terminal 283 and consequently to variable limiting resistor 236 turns the silicon controlled rectifier 241 on by the action of current flowing into gate 242 equaling or exceeding the minimum firing current of the silicon controlled rectifier 241. The thyristor or silicon controlled rectifier 241 remains on and allows current to flow through relay coil 250 thus energizing it causing a slaved circuit control means such as normally open contact 250KA to close starting timer 272 and normally closed contact 250KB to open. The significance of these relay contacts and their function in the circuit will be described subsequently. The previously referred to undulating or poorly filtered current flowing from terminal 197? to terminal 197N of bridge rectifier network 197 through terminals 286 and 284 of timing circuit 190 causing the conducting silicon controlled rectifier 241 to turn off due to the undulation or lowering of the supply voltage once every half cycle. The effect of this would be to allow current to flow through relay coil or signaling means 250 for a significant but not entire part of every complete cycle. Were it not for the presence of capacitor 254 and diode 260, the coil 250 would be deenergized immediately upon turn off of the silicon controlled rectifier 241. However, the initial charging of capacitor 254 due to the presence of power for one half cycle at terminals 286 and 284 energizes capacitor 254 to such an extent that when silicon controlled diode or gate 241 turns off, the charged capacitor 254 retains energizing voltage across the relay coil 250 keeping it energized. As current 12 ceases to flow, any current which would have been induced into current transformer 163 ceases and the voltage drop across the resistance elements 224 through 230 changes to a value near zero, thus removing the source of turnon current from terminal 283 and gate 242 of silicon controlled rectifier (SCR) 241. A short time after this, in relationship to the time constant of the diode 260, intrinsic resistance 252, and capacitor 254, the voltage across coil 250 becomes less than the necessary energizing voltage of coil 250 thus deenergizing coil 250 and causing contacts 250KA and 250KB to change their relative conducting states. Contact 250KA will open stopping timer 272 and contact 250KB will close. As long as current 12 continues to flow in the secondary 154, the time constant of the combination of diode 260, intrinsic resistance 252 and capacitor 254 is such that the voltage across said capacitor will not decay to the minimum energizing voltage or actuating potential of relay coil 250 before the next complete cycle of gate current flows or surges into gate 242 thus turning thyristor or SCR 241 on again, reenergizing coil 250 from source 197 and recharging capacitor 254 to a nominal 28 volts. This has the effect of maintaining coil 250 in the energized or on" state continuously as long as current is flowing in secondary coil or winding 154, even though the silicon controlled rectifier 241 is off for a significant part of each cycle.

As previously mentioned, relay or coil 250 has two contacts 250KA and 205KB which are actuated by energizing coil 250. Upon energization of relay coil 250, normally closed contact 250KB opens to disconnect light or lamp 268, from secondary winding 191B to thereby deenergize lamp 268. Conversely, when contact 250KB is closed, lamp 268 is energized indicating that the secondary current 12 in winding 154 of transformer 142 has ceased to flow or an open circuit exists at the terminals 159 and 161. Concurrently with this, contact 250KA is closed, thus energizing timer 272. When coil 250 is deenergized, contact 250KA opens stopping the timer 272. Timer 272 measures accurately within approximately one cycle the time that current 12 flows in secondary coil or winding 154 of transformer 142. Resistor 274 and capacitor 276 form a pulsesuppression network which is connected in parallel with contact 250KA and used to suppress induced spikes of voltage upon the closing and opening of contact 250KA. Although not shown, other contacts of the relays of the tester may be provided with similar suppression networks, since it is desirable to prevent the electromagnetic radiation of high frequency energy which may cause the digital voltmeter (DVM) readout to give false indications or false readings during the opening and closing of such contacts.

A method for determining the maximum current which has flowed during a small period of time and the period of time for which it has flowed is provided by the primary embodiment of this invention. Referring to FIG. 2, it will be noted that voltmeter 172 is connected to output terminals 282 and 281 of current conversion control means 165. This meter gives an indication of the amount of current in secondary winding 154 at any time. Voltmeter 172 is calibrated to give an accurate reading. Switching circuit 234 prevents an overvoltage condition on voltmeter 172 by allowing an operator to change the amount of voltage present at terminals 281 and 281A as the current in secondary circuit 154 becomes larger merely by changing the position of switch 234. Placement of movable contact 234W to tap 232A and insertion of conducting link 244L is used when near maximum 12 flows. Conducting link 244L bypasses the resistance combination 224 removing it from the circuit. Voltmeter 172 however has a mechanical movement which is rather slow to react to quick current charges. Therefore, a digital voltmeter 174 with a voltage holding circuit and an oscillograph 176 preferably of the light beam type, but not limited to that type, is connected in parallel with voltmeter 172 to terminals 281 and 281A. Both devices are connected to sense the presence of voltage and the oscillograph will self-actuate upon the presence of some minimum value of voltage. Such voltage is created at the first surge of current in secondary winding 154. As this voltage is detected by digital voltmeter 174 and oscillograph 176, both devices begin to record. Oscillograph 176 records the analog shape of the curve of the voltage, but more particularly it is very accurately calibrated with respect to time so that the actual time of current flow in secondary winding 154 can be measured subsequent to the recording. Concurrently, digital voltmeter 174 with its holding circuit (usually standard in most digital voltmeters) retains the highest voltage reached during the surge of current in secondary circuit 154. Therefore, the time that the surge of current has flowed and the maximum value of the current surge is recorded in real time and retained for future study even though the current may have flowed for such a small period of time as not to actuate the movement of meter 172 or the timing circuit 190. This is the situation which usually prevails when a circuit breaker 164 under test trips or opens almost immediately upon the application of current. Such a situation exists when an instantaneous type magnetic trip overload test for circuit breaker 164 is conducted. By measuring the amount of time elapsed as recorded on the oscillographic record against a calibrated time scale which is available on almost all types of oscillographic recorders and by recording the highest voltage obtained on the digital voltmeter 174 and converting it to current, the maximum current and time of flow for any circuit breaker under test can be measured and preserved. The use of a simple voltmeter such as 172 would not show the maximum flow of current because of the inherent momentum or inertia of the movement of the meter.

Finally, push-button or switch 212 which is connected to the secondary 191B of transformer 196T is the switch which controls the shunt trip coil 214 of circuit breaker 114 such that power to the entire circuit breaker testing means 107 can be removed merely be depressing switch or push-button 212, energizing coil 214 and opening circuit breaker 114 through the use of its shunt trip coil 214. Naturally, the circuit breaker 114 has suitable series current sensing or trip coils (not shown), which will cause the circuit breaker to trip should any current overload exist in the primary circuit of transformer 142 or the attendant transformer circuits. The series trip coils of the circuit breaker are not shown since the operation of such means is well known in the art of circuit breakers.

1t is to be understood that although single phase power from power source is illustrated as the input power to the the circuit breaker 114, it is possible to use multi-phase alternating current power as an input for the circuit breaker tester 107 and to use combinations of testers 107 in different testing arrangements. It is also envisioned that any of the resistive components indicated in current conversion and control means 165 can be of any degree of accuracy and can be arranged in either shunt or series circuit relationship to obtain the desired degree of accuracy including the use of more than the four main resistive components 224, 226, 228 and 230. It is also to be understood that the device to be tested need not necessarily be a circuit breaker or interrupter but may be any device whose characteristic current-versus-time relationship is to be determined and which has a maximum current level within the range of the current generating capacity of the present invention. It is also to be understood that the differential output autotransformer 118 as shown in FIG. 2 may be of the single ended variety such as autotransformer 18 in FIG. 1 where desired. It is also to be understood that full wave bridge rectifier 197 may be replaced by a half-wave bridge rectifier. In addition, the positive and negative terminals 197T and 197N of rectifier network 197 may be reversed where circuit elements energized by said network may be of the type that requires undirectional current flow in the opposite direction than shown or indicated in FIG. 2. If necessary, two bridge rectifier networks one generally corresponding to bridge network 197 and another with the opposite polarity may be used in conjunction with transformer 196T to supply power to elements in circuit breaker tester 107 which may require differing directions of current flow depending upon the particular element. A triac or bidirectional gated element may be used in place of thyristor or SCR 244 as shown in FIG. 2, if the use of one particular type of power supply makes it desirable to do so.

The apparatus embodying the teachings of this invention has several advantages. First, main transformer 142 is the only transformer which normally carries the full amount of power as transferred by circuit breaker 114, while autotransformer 118 only carries the full amount of power in the very lowest ranges of power when a very low current is sought to be provided in secondary winding 154. This means that autotransformer 118 can be a relatively low power device and that the fine control that is necessary in testing circuit breakers can be accomplished by the use of the variable autotransformer or Variac with the boosting transformer. The boosting transformer supplies a continuous voltage between zero and some maximum value which can be used to increase the current in secondary winding 154 continuously between the incremental steps made available by the use of the array of three bus bars and three windings in the primary 143 of transformer 142. In addition, current duration during circuit breaker tests can be measured quite accurately by the use of the current timing means l90with an error of no more than one cycle. Also, a method has been developed to test instantaneous flow of current to determine its maximum amount and the time it has flowed notwithstanding the fact that high momentum or inertia meters or measuring instruments could not detect the maximum current nor could the standard timing device be used to time it. A further advantage of the invention is the fact that it can be adaptable to various commercially available voltage ranges such as 208, 240, 440, and 550 volts alternating current. Of practical importance is the fact that the tester can be made a light weight device and also can be made less expensively. The operation of the circuit is very simple and its setup is relatively simple or convenient, as an operator merely needs to energize said device by connecting into a commercially available power outlet and turning on or energizing the equipment after having ascertained the values of current to be applied to the circuit interrupter under test and having set the three movable partially insulating conducting slugs between the various fine control and coarse control windings of transformer 142 and their associated common bus bars.

I claim:

1. A portable circuit interrupter testing means adapted to be connected to a power supply with output terminals, comprising a first transformer including a primary winding which in turn includes a plurality of primary winding sections, said primary winding including primary winding terminals, each of said primary winding sections including a plurality of primary turns, also said first transformer including a secondary winding adapted to be connected to a load, a second transformer with a primary winding and a secondary winding, and a power dividing means having a set of output terminals and a set of input terminals adapted to be connected to said output terminals of said power supply means, said secondary winding of said second transformer having first and second terminals, said first terminal of said secondary winding of said second transformer being adapted to be connected in series circuit relationship with one terminal of said primary winding of said first transformer, said second terminal of said secondary winding of said second transformer being adapted to be connected to one terminal of said power supply means, portions of said primary winding of said second transformer being adapted to be selectively connected in parallel or series circuit relationship with said set of output terminals of said power dividing means, another of said terminals of said primary winding of said first transformer being connected to another output terminal of said power supply means.

2. The combination as claimed in claim 1, wherein said power dividing means comprises an autotransformer means, said primary winding of said first transformer being adapted to have one or more primary winding sections selectively connected in series or parallel circuit relation to thereby vary the total number of primary turns included in said primary winding.

3. The combination as claimed in claim 2, wherein said winding sections of said primary winding of said first transformer include tapped contacts between discrete groups of winding sections, a plurality of bus bars, a separate connecting electrically conducting means, said primary winding sections of said first transformer being accessible to said plurality of bus bars such that said tapped contacts are adapted to be selectively connected by said separate connecting conducting means to said bus bars to thereby connect a plurality of said discrete groups of winding sections in series or parallel circuit relationship, a constant load current sensing means disposed adjacent to said secondary winding of said first transformer.

4. The combination as claimed in claim 3, wherein said autotransformer means includes an autotransformer and two ganged moving contactors, said autotransformer having two windings disposed in series circuit relationship each having a plurality of turns said autotransformer conducting significantly less than the full power current required by said first transformer, said set of output terminals of said autotransformer means being connected to one fixed terminal each of said two ganged moving contactors the moving terminals of which are disposed to engage the turns of the latter windings, said tapped contacts of said primary winding of said first transformer being arranged in three arrays, two of said arrays being adapted to provide relatively small variations in the number of said turns in said primary winding of said first transformer and one said array being adapted to provide relatively large variation in the number of said turns, each said array having a movable metallic means for use in connecting said tapped contacts to said associated bus bars, said secondary of said first transformer being adapted to provide output current when connected to a load, said current sensing means comprising a current transformer, a current conversion and control means connected to said current transformer, a switching means, a set of system output terminals and a measuring means, said switching means connecting said current conversion and control means to said measuring means and said system output terminals, a starting switch, said output current flowing in said secondary of said first transformer when con nected to a load after engaging said starting switch.

5. The combination as claimed in claim 4, said current transformer being disposed to respond to the output current of said secondary winding of said first transformer, said current conversion and control means including a plurality of resistance means to provide uniform electrical resistive load to nected in a circuit relationship to said switch output terminals, said current conversion and control means being adapted to provide an alternating voltage signal through said switch to said system output terminals which signal varies with the amount of current flowing in said secondary of said first transfonner. 

1. A portable circuit interrupter testing means adapted to be connected to a power supply with output terminals, comprising a first transformer including a primary winding which in turn includes a plurality of primary winding sections, said primary winding including primary winding terminals, each of said primary winding sections including a plurality of primary turns, also said first transformer including a secondary winding adapted to be connected to a load, a second transformer with a primary winding and a secondary winding, and a power dividing means having a set of output terminals and a set of input terminals adapted to be connected to said output terminals of said power supply means, said secondary winding of said second transformer having first and second terminals, said first terminal of said secondary winding of said second transformer being adapted to be connected in series circuit relationship with one terminal of said primary winding of said first transformer, said second terminal of said secondary winding of said second transformer being adapted to be connected to one terminal of said power supply means, portions of said primary winding of said second transformer being adapted to be selectively connected in parallel or series circuit relationship with said set of output terminals of said power dividing means, another of said terminals of said primary winding of said first transformer being connected to another output terminal of said power supply means.
 2. The combination as claimed in claim 1, wherein said power dividing means comprises an autotransformer means, said primary winding of said first transformer being adapted to have one or more primary winding sections selectively connected in series or parallel circuit relation to thereby vary the total number of primary turns Included in said primary winding.
 3. The combination as claimed in claim 2, wherein said winding sections of said primary winding of said first transformer include tapped contacts between discrete groups of winding sections, a plurality of bus bars, a separate connecting electrically conducting means, said primary winding sections of said first transformer being accessible to said plurality of bus bars such that said tapped contacts are adapted to be selectively connected by said separate connecting conducting means to said bus bars to thereby connect a plurality of said discrete groups of winding sections in series or parallel circuit relationship, a constant load current sensing means disposed adjacent to said secondary winding of said first transformer.
 4. The combination as claimed in claim 3, wherein said autotransformer means includes an autotransformer and two ganged moving contactors, said autotransformer having two windings disposed in series circuit relationship each having a plurality of turns said autotransformer conducting significantly less than the full power current required by said first transformer, said set of output terminals of said autotransformer means being connected to one fixed terminal each of said two ganged moving contactors the moving terminals of which are disposed to engage the turns of the latter windings, said tapped contacts of said primary winding of said first transformer being arranged in three arrays, two of said arrays being adapted to provide relatively small variations in the number of said turns in said primary winding of said first transformer and one said array being adapted to provide relatively large variation in the number of said turns, each said array having a movable metallic means for use in connecting said tapped contacts to said associated bus bars, said secondary of said first transformer being adapted to provide output current when connected to a load, said current sensing means comprising a current transformer, a current conversion and control means connected to said current transformer, a switching means, a set of system output terminals and a measuring means, said switching means connecting said current conversion and control means to said measuring means and said system output terminals, a starting switch, said output current flowing in said secondary of said first transformer when connected to a load after engaging said starting switch.
 5. The combination as claimed in claim 4, said current transformer being disposed to respond to the output current of said secondary winding of said first transformer, said current conversion and control means including a plurality of resistance means to provide uniform electrical resistive load to said secondary of said first transformer, said plurality of resistance means having tapped output terminals, said switching means being a switch having a plurality of input contacts and a set of switch output terminals, each said tapped output terminal being connected to an input contact, said switch thereby being adapted to connect one of said resistance means tapped output terminals with one of said switch output terminals, said measuring means and said system output terminal being connected in a circuit relationship to said switch output terminals, said current conversion and control means being adapted to provide an alternating voltage signal through said switch to said system output terminals which signal varies with the amount of current flowing in said secondary of said first transformer. 